Potential Causes & Sources

A cause is an event, agent, or series of actions that produces an effect.  In the context of a watershed management plan, the effect is the problem.  Potential causes were identified for each problem statement based on the information summarized in the Watershed Inventory in Section 2.  Where applicable, potential causes were related to specific pollutant parameters identified during the Watershed Inventory.  A source is an activity, material or structure that results in nonpoint source pollution.  Potential sources were identified for each problem statement based on the information analyzed in the Watershed Inventory in Section 2.  Table 48 lists the potential causes and sources for each problem.

It should be noted that a non-active construction site is considered to be a site that has been hydrologically altered (e.g. trees have been cleared, topsoil/vegetation has been stripped) and the site is just bare ground with no permanent erosion control measures in place.

Pollutant Loading

Current Loading Calculation Methodology

Nitrate + Nitrite, Total Phosphorus, E.coli and Total Suspended Solids were identified as potential causes for several of the problem statements.  In order to determine the extent of the current problem, current loads must be determined for comparison to target or known water quality targets.

There are several ways to estimate the current pollutant loads in a watershed, including nonpoint source modeling and actual sampling data.  Both sources of information are available for the Geist Reservoir/Upper Fall Creek Watershed.  With the extent of water quality data available from IDEM data and the CIWRP study, it was determined that the most accurate estimate would incorporate the available water quality data rather than the modeling results.

Two data sets, IDEM (2008-2009) and CIWRP (2003), sampled for Nitrate + Nitrite, Total Phosphorus, E.coli and TSS.  Instead of averaging these two data sets together, the IDEM data was used for this calculation as it was the most recent data available.  The mean value of each parameter was calculated on a subwatershed-wide scale.

For the purposes of a watershed management plan, the pollutant loads need to be calculated in either pounds per year or tons per year.  Since the water quality data was provided in units of mg/L and CFU/100mL, a flow rate was needed for the conversion.

There is one USGS gaging station located within the Geist Reservoir/Upper Fall Creek Watershed.  The station, number 03351500, is located on Fall Creek near Fortville.  Average annual flow data is available for this station from 1942-2008.  At the gage site, the drainage area is 169 square miles and the average annual flow is 182.1 cfs.  This flow was scaled to each subwatershed.

IDEMs load calculation tool was then used to estimate the loads based on the flow and concentration data.

Target Loads

The target loads were identified based on known water quality guidelines or standards for each pollutant.  These standards typically reference a concentration, therefore as described above, IDEMs load calculation tool was used to estimate the target loads based on the flow and standard concentration data.

The single sample state standard in Indiana for E.coli is 235 CFU/100 mL.

Levels of Total Nitrate and Nitrite greater than 10 mg/L exceed the water quality standard for Nitrate and Nitrite as described in the Indiana Administrative Code (IAC).  However, for this analysis, a target of 1.6 mg/L was identified as the EPA nutrient criterion for this eco-region.

Levels of Total Phosphorus greater than 0.3 mg/L exceed the IDEM statewide draft TMDL target, while levels above 0.076 mg/L exceed the EPA recommended water quality targets.  For this analysis, EPA’s recommended maximum was used as the target.

Levels of TSS greater than 30 mg/L exceed the IDEM statewide draft TMDL target.

Load Reductions

Once the current loads and the target loads of each pollutant were determined, the required load reduction to meet the targets was calculated.

Tables 49-51 show the current, target and reduction loads of E.coli, Nitrate+Nitrite and Total Phosphorus within the watershed.  Since the current TSS concentration was less than the target in eight of the nine subwatersheds, no reduction is required in these subwatersheds.

The Deer Creek Subwatershed averaged higher than the target in TSS at 31.9 mg/L.  The current load of the Deer Creek Subwatershed was calculated to be 954.0 ton/year.  With the target of 30 mg/L or 897.2 ton/year, the reduction required is 56.8 ton/year, or 6.0% for this subwatershed.

Only IDEM E.coli values were used to create Table 49.  CIWRP data exists for this parameter, however, the IDEM data is more recent.  Thorpe was not measured for E.coli based on the most recent IDEM data.  There is older data from CIWRP, but it was not used in the creation of this table since the values were much larger than the IDEM data and the IDEM data is showing exceedances in all subwatersheds.